1. Field of the Invention
The present invention relates to ink-jet recording, particularly to an ink-jet recording method capable of obtaining a high quality image on a recording medium mainly comprising plain paper, and to an ink-jet ink (abbreviated as “ink” hereinafter) used thereto. The invention further relates to an ink-jet recording unit, ink cartridge for ink-jet recording and ink-jet recording apparatus.
2. Description of the Related Art
The ink-jet recording method is the method of ejecting small droplets of ink by applying energy, and recording by landing the droplet on a recording medium such as paper. Particularly, in the method using an electricity-heat conversion member as an ejection energy supply device for ejecting the droplets by allowing bubbles to be generated by applying a heat energy to the ink, a recording head is readily made to have high density nozzles to enable high resolution quality images to be recorded in a high speed (see Japanese Patent Publication Nos. 61-59911, 61-59912 and 61-59914).
However, since the conventional ink used for ink-jet recording usually comprises water as a principal component with supplemented water-soluble high boiling point solvents such as glycols for preventing drying and clogging the ink permeates deep into the recording paper when images are recorded on plain paper using such ink. Consequently, sufficient image densities cannot be obtained, and the quality of black letters are deteriorated and image densities become uneven probably due to uneven distribution of fillers and sizing agents on the surface of recording paper.
The above-mentioned problem can be solved by, for example, adjusting the pH of the ink above 12, or controlling the surface tension of the ink to be higher than the critical surface tension of the recording medium (Japanese Patent Publication No. 63-2996). Although the problems of the image density, clearness and the quality of black letters may be solved by recording with the ink described above, a problem of safety still remains while the ink is not suitable for high speed printing due to insufficient fixing speed.